
VOLUMETRIC STUDIES OF THE FOOD 
AND FEEDING OF OYSTERS ^ ^ > 



From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXVIII, 1908 



Proceidi7igs 0/ tlie fourth International Fishery Congress 



Washington, igo8 




WASHINGTON 



: : GOVERNMENT PRINTING OFFICE 



1910 



VOLUMETRIC STUDIES OF THE FOOD 
AND FEEDING OF OYSTERS ^ ^ ^ 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXVIII, 1908 
Proceedings of the Fourth International Fishery Congress : : Jlashington, ipoS 




\'\W\r' 



^x. 



WASHINGTON :::::: GOVERNMENT PRINTING OFFICE 



: : 1910 






BUREAU OF FISHERIES DOCUMENT NO. 719 

Issued May. 1910 



D. OF D. 

IV;A/ ic 1910 



I 
d 



VOLUMETRIC STUDIES OF THE FOOD AND FEEDING 
OF OYSTERS 



By H. F. Moore 

Assistant, U. S. Bureau of Fisheries 



Paper presented before the Fourth International Fishery Congress 
held at Washington, U. S. A., September 22 to 26, 1908 



VOLUMETRIC STUDIES OF THE FOOD AND FEEDING 
OF OYSTERS. 



By H. F. MOORE, 
Assistant, United States Bureau of Fisheries. 



Economically considered, probably the most important direct interrela- 
tion between a marine animal and plants is that existing between the oyster and 
its food. We have in the United States alone an industry valued at $18,000,000 
per annum, which is immediately dependent upon the supply of microscopic 
vegetation in our bays and estuaries, a vast food resource useless to man in its 
original state, but of great present and still greater potential value when trans- 
substantiated into the flesh of oysters, clams, and other moUusks. 

Various investigations have shown that about 95 per cent of the food of the 
oyster consists of diatoms and that most of the remainder is composed of other 
equally minute plants or organisms on the more or less debatable borderland 
between plants and animals. The oyster obtains these microscopic organisms 
by drawing feeble currents of water between the open shells, straining them 
through the exceedingly minute orifices in its gills, and passing the filtrate by 
ciliary action into its mouth, which lies ensconced between two pairs of fleshy 
palps close to the hinge of the valves. Though the currents induced are feeble 
they are constant, and during the course of twenty-four hours the water thus 
minutely strained is many times the volume of the oyster. 

It is common knowledge among oystermen and oyster growers that differ- 
ent localities differ markedly in their powers or capabilities for growing and fat- 
tening oysters, and the results of various researches have shown that these 
diversities are correlated with the amount of food available to the sessile oys- 
ters. A deficiency may be due to a natural poverty of the waters, to an over- 
population of oysters, or to an absence of currents sufficient to carry the food 
within reach of the feeble external currents set up by the oysters themselves. 
Frequently all three of these factors are found to be involved where oysters grow 
slowly and fail to fatten. 



1298 BULLETIN OF THE BUREAU OF FISHERIES. 

Certain enthusiasts, some of whom should know better, have held forth the 
prospect of a time when the entire available bottom of our bays and sounds 
would be planted in oysters as densely as are the comparatively small areas now 
utilized. They fail to consider the fact that the natural fertility of the waters 
imposes some limit upon the production of oyster food, and that a vast increase 
in the oyster population, such as their imaginations contemplate, would undoubt- 
edly exceed the limits which nature has set. 

The microscopic vegetable life of our brackish bays and sounds is probably 
as abundant as it is capable of becom.ing under existing conditions. It is depend- 
ent primarily upon the quantity of certain mineral salts in solution, and is as 
strictly limited by the conditions as is the crop yield of a given area of land by 
the available salts in the soil. The soils can have their fertility artificially 
increased, but though experiments conducted by the author for the Bureau of 
Fisheries have shown that the same expedient is partially successful for limited 
areas of inclosed water, it can never be applied to open waters, as the fertilizer 
would be speedily carried away. In this connection, however, it is an interesting 
speculation whether our coastal waters are not to-day richer in fertilizing salts 
than they have been in the past. The denudation of our forest lands, the 
erosion due to faulty agriculture, the artificial fertilizers carried away from 
cultivated fields during periods of heavy rainfall, and the discharge of sewage rich 
in organic matter have undoubtedly added much to the available fertilizing 
content of our coastal waters, to the advantage of their microscopic vegetation. 

The question of food supply, its availability, and the quantity required for a 
given area planted in oysters is one of vital importance to the oyster culturist. 
Of the total oyster supply of the United States, about five-eighths, valued at 
over $10,000,000, is produced on planted beds, and the future growth of the 
industry is dependent upon the increase of the area of private bottoms under 
culture. With the extension of the planting industry to new localities and the 
inevitable congestion in places naturally favorable for growing and fattening 
oysters, the value of definite data upon this subject will be greater in the future 
than in the past. 

Empirical methods involving actual planting to determine the suitability of 
a locality are expensive and often wasteful, and operators with small capital are 
frequently deterred from taking the risk. Even though the work on a small 
scale may prove successful, an increase to a large commercial basis may overtax 
the food supply to such an extent as to make the growth of the oysters slow and 
their fattening impossible. A number of cases of this kind have come to the 
author's attention, the most noteworthy being in Lynnhaven Bay, where the 
increase in the area planted, though the quantity per acre is exceedingly small, 
has made it almost impossible to fatten oysters properly on certain bottoms 
formerly satisfactorj'. 



FOOD AND FEEDING OF OYSTERS. 1 299 

As the economic importance of the subject merits, it has frequently been the 
matter of investigation and has probably attracted more attention from biolo- 
gists than has any other direct correlation between marine plants and animals. 
The nature of the oyster's food was long ago determined and the work of the last 
twenty years has been hardly more than confirmatory of that which preceded it. 

Dean appears to have been the first to attempt the quantitative determination 
of the oyster food available in the water. He employed a chemical analysis 
of the water to determine the albuminoid ammonia content, assuming that the 
results would indicate the comparative food values of different regions. 

Subsequent investigators have recognized the grave defects in this method, 
and, including myself, have all followed the general method of Rafter. Water 
specimens of definite volume, usually i liter, have been collected either by means 
of a stoppered bottle or jug, from which the cork is pulled after it has been sunk 
to the bottom, or by a specially designed metal cylinder constructed on essen- 
tially the same principle. The suspended matter in the specimen, a large part 
of which often consists of sand, mud, and debris, is then concentrated in, say, 
ID cubic centimeters of water by filtration through sand or precipitation in an 
Erlenmeyer flask after the addition of a few drops of formalin. A definite quan- 
tity of the filtrate is then removed after agitation and the food organisms counted 
in a Rafter cell, the calculated number of such organisms per liter being regarded 
as an expression of the food value of the water. 

This method has two defects, the first of which is that the water specimen is 
not drawn from the stratum tenanted by the oyster, but solely from a height of 
about 12 inches above the bottom. It would be possible to correct this defect 
by using a shorter, broader bottle or specimen cup, but as the water flows rather 
slowly into the necessarily narrow inlet, there would enter with it a considerable 
quantity of material stirred up when the instrument strikes the bottom. As 
the amount of this material would vary with the bottom, the impact, Mid the 
currents, a more serious source of error would arise and the results would become 
worthless. 

To obviate these difficulties I have designed the type of bottle illustrated in 
text figures i to 5. It consists essentially of a brass barrel of a capacity somewhat 
over I liter, two conical valves, and a tripping device. The lower valve is fixed 
at a height of 2 inches above a broad base, which prevents the instrument from 
sinking in soft mud, but the barrel and upper valve slide freely on a central 
column or rod. The instrument is set by engaging the lug (F) over the inclined 
surface (G) of the stirrup or tripping device (CDEG), which suspends the 
upper valve (B) and the barrel (A) so as to leave a gap of 2 inches between the 
two valves and their respective seats, the stirrup being maintained in position 
by tension on the cord by which the instrument is lowered. By rotating the 
cam (H) so as to pinch the cord between it and the collar on top of the upper 



I300 



BULLETIN OF THE BUREAU OF FISHERIES. 



valve, the instrument may be locked in the set position, but it is automatically 
unlocked when it is raised by the cord. 

As the instrument is lowered there is a free flow of water through the barrel, 
so that at any given time its contents are taken from the stratum in which it 





^/<f//i7//a/7. 



s5<Tc//o/^f. 



rests. When bottom is touched the tension on the cord is relaxed, the tripping 
device instantly releases the upper valve and the barrel suspended from it, and 
they fall into their respective seats, inclosing a sample of water before it can be 
contaminated by the stirred-up bottom deposits. As the barrel is lo inches 



FOOD AND FEEDING OF OYSTERS. 



1 301 




Fig. 3 . — Cross section 
at A. figure 2. 



long, the water inclosed is a vertical column of the stratum lying between 2 
inches and 12 inches above the bottom, and as the currents do not flow over 
the beds in horizontal strata, but roll over and over, this specimen is regarded 
as a fair sample of that in which the oysters are bathed. 

The instrument is now used in Massachusetts, Maryland, Virginia, and Loui- 
siana, and actual tests have shown that it takes a water speci- 
men much cleaner and freer from mud and extraneous materials 
than do the instruments previously employed. 

The other defect of the old method of determining the food 
value of oyster-producing waters arises from the practice of using 
the number of diatoms or organisms per liter as the measure 
of their productiveness. It is well known that diatoms, which 
usually constitute upward of 95 per cent of the food of oysters, 
differ greatly in size and the species vary in comparative abund- 
ance in different regions and from season to season in the same locality. When a 
numerical expression is employed, it follows therefore that a multitude of small 
organisms may give an apparent superiority to a water specimen as compared 

with another containing a 
o/) /e/yo/"^ smaller number of a spe- 

cies of vastly larger size and 
much greater aggregate vol- 
ume, and my own ex- 
perience has shown cases 
where this error amounted to 
nearh' 400 per cent. The 
method is attended with 
grave error as applied to 
even limited regions and is 
wholly untrustworthy as a 
basis of comparison between 
widely separated localities. 
It gives seemingly quanti- 
tative results, but these, not 
being volumetric, are decep- 
tive. 

Direct volumetric deter- 
mination can not be made 
on account of the presence 
of considerable volumes of sand, mud, and extraneous debris in the filtrate, 
these materials greatly exceeding the food organisms in volume. Grave 
attempted to overcome the difficulty by listing the food organisms by species, 






SaM3/77jy/<rfr<i/' ^ 



Details of tripping device of water specimen cup in figures i and : 



I302 BULLETIN OF THE BUREAU OF FISHERIES. 

but this arrangement, though an advance on previous work, is not capable of 
comparative use, and any error in identification, not unHkely to occur with 
persons not diatomists, would be misleading to future investigators. 

To overcome these difficulties I have for several years used the following 
indirect method, which has given satisfactory results. The diatoms and other 
food organisms are collected and counted, as before indicated, and are listed by 
species, although their identification by their correct names is not essential. 
Careful outline camera lucida drawings are made of the zonal and valvular 
aspects of a number of specimens of each species, and their cubic contents are 
calculated by geometric methods from planimeter measurements of the draw- 
ings. The average of a number of such calculations will give the average rela- 
tion of the volume to the product of length, breadth, and thickness of the 
species. Using this relation and the average of a number of micrometer meas- 
urements of the specimens themselves, a simple calculation will furnish an 
approximately correct expression of the average volume of the species in the 
region under investigation. If these volumes be employed as multipliers into 
the numbers of the respective species, determined from the counts in the Rafter 
cell, we have an approximately correct volumetric expression for the amount 
of the food content of each specimen of water. As the most convenient unit of 
measurement I have adopted Van Heurck's "c. d. m." (o.oi millimeter), the 
unit of volume being the cube of this, "cu. c. d. m." (0.000,001 cubic milli- 
meter) . The following is an illustration of the data required for each species : 

Synedra commuiata (Matagorda Bay) ; average length, 4.7 c. d. m. ; breadth, 
0.5 c. d. m.; thickness, 0.5 c. d. m.; volume = 0.6 (1 X b X t) =0.7 cu. c. d. m. 

This method sounds elaborate in its narration, but has not shown itself to be 
cumbersome in practice, and, moreover, it appears to be the only method so 
far proposed which gives data of real value. The results are directly compar- 
able with those obtained in other waters or with those reached in the same 
waters at different seasons. Five hundred or 600 determinations have been 
made in the past two years, and, for reasons shown below, the procedure gen- 
erally was found to require but little more labor than the older misleading and 
less accurate method. 

In oyster investigations it is customary to take a large number of water 
specimens at adjacent stations, and as the nature of the food content of each 
varies in quantity rather than in the character of the organisms, the measure- 
ments of eight or ten species will apply to all water samples from the locality. 
Only those organisms need be measured which examinations of the stomach 
contents of the oysters show to be important as food. The counts have to be 



FOOD AND FEEDING OF OYSTERS. 



1303 



made, whatever method be employed. In Matagorda Bay, where the present 
method was first used, about 150 specimens of water were examined and the 
additional time required was not over 10 per cent. The following table shows 
the results and the manner of tabulation, as well as the differences in results 
attained by the numerical and the volumetric methods : 

Food Value of Waters op Matagorda Bay." 
[Roman figures indicate volume of organisms, or food value. Bold-face figures indicate number of organisms.] 



No. 


Species. 


A. 

Between 

Sand and 

High 

Mound 

signals. 


B. 
Between 

High 

Mound 

and Lake 

'signals. 


C. 

Between 

Mad Island, 

West, and 

Lake 

signals. 


D. 
Between 

Shell 
Island and 
Mad Island 

reefs. 


E. 

Between 

Dog Island 

and Shell 

Island 

reefs. 


F. 
Between 
Dog Island 
and Pa- 
vilion 
signal. 






i 


500 

121,80s 
3,483 

1,750 

^■37! 

'■m 
2I 

250 




917 

'■* 4,081 
17.760 
2.960 

8<6 
4. 160 
416 
1.688 
675 
6=5 
125 
125 
125 


250 

2,000 
1,000 

li5o 


100 

'"4.650 






lineatus _ _ 


141,470 
4.042 

6,413 

683 

1,660 
166 

1. 145 
458 


'^i'lSS 


3 




3.500 




2,000 












'Too 
i5o 

100 
426 


5'?S2 


6 


arenaria 

Amphora ovalis 


500 

'■5S0 


'/ 








8 








9 












125 
375 






225 
350 


500 






292 


125 


1,250 














1 
I 

{ 

{ 


5, 600 
8.000 

250 


6,650 
9,500 

68,340 
3,417 


IS',000 

i',083 

675 


sei^o 
■1^0 


8. 155 
11.650 

"^'650 

18,160 

908 


J.-iS2 


14 




875 
250 




16 














200 
300 








{ 


1,250 

'kill 


600 


292 

8.7SO 
1,260 


250 

8.7SO 
1,250 


1,000 












Total volume, or food value _ _ 

Total number of organisms 












219.342 
23,108 


273.861 

26,416 


271. 743 

30,393 


284.050 
51,750 


177.640 
20,083 


166, 52s 

13,260 




208.527 
259. 774 
190,049 


287,737 
345. 200 
188,450 


239.024 
267.000 
314.412 


259.875 
274.350 
317,625 


159,937 
177.900 
193. 770 


89,92s 
254.92s 
'53. 72s 




Middle of bay 











I From Survey of Oyster Bottoms in Matagorda Bay, Texas, by H, F. Mo 



of Fisheries Document 61 



I304 



BULLETIN OF THE BUREAU OF FISHERIES. 

Food Value of Waters of Matagorda Bay — Continued. 



No. 


Species. 


G. 
Between 

Pavilion 
and Three- 
mile sig- 
nals. 


H. 
Between 
Three-mile 
and Seven- 
mile sig- 
nals. 


I. 
Between 
Seven- 
mile and 
Grass 
signals. 


J. 
Between 
Grass and 
Dressing 

Point 
signals. 


K. 

Live Oak 
Bay. 


L. 

Above 

Dressmg 

Point. 




rt 


/ 


875 


292 

163.310 
4,666 

"Mo 

Ji2 

'■•ilo 

166 


792 

''5,666 
' 2,667 

1.458 

583 


200 

118,720 
3,392 
9, 150 
1,525 

'''isi 






3 




157. 500 
4,500 


140,000 
4,000 






3 




583 






















^'iio 






5 






■250 






i',000 

830 

166 


3. 750 
1,.500 

3.7SO 
750 


•2',167 
1, 66s 










333 






8 
9 


166 
125 
166 
166 
167 
642 
917 
sSi 
166 

1,000 
167 
125 


166 








750 


260 








492 

883 


583 


lO 


teniii'^ciimum 




1,500 
125 

962 
1,375 

\Mo 

'°'500 
250 
250 


750 
166 

I. 793 
541 


750 


883 




angulata major 

Synedra coramutata -- 

sp -- 




13 

14 


1.686 
2,408 
4.812 
1,375 

208 
100 
517 

14.581 
2,083 


2\MS 
V,55o 


I. 166 
1,666 

'3,166 












sp- -- 

Pyxilla sp 


542 
167 
125 




333 




750 
2,250 

=ilo 






500 


19 






2.62s 
375 


\,tu 


11,669 
1,667 


Total volume, or food value 

Total number of organisms 




178.275 
14.750 


194.600 

13.832 


260. s8o 
15,540 


167. 792 
15,207 


'WMh 


181.586 
16,964 




1S1.050 
186,599 
189.67s 


162. 900 
.82.925 
238.349 


191. 700 
357. 650 
232. 250 


182,470 
152.525 
168.674 































In the study of the food actually consumed by the oyster, it has been 
regarded, heretofore, as sufficient to remove the stomach contents by means of 
a pipette inserted in the mouth or through an incision in the body walls. This 
method extracts but an indeterminate portion of the undigested food in the 
stomach, a considerable proportion remaining in the folds of that organ and in 
the wide openings of the hepatic ducts, and it removes practically nothing of 
the intestinal contents. For quantitative work the method is very defective, 
and it is useless as a basis for those studies of food consumption and the rate of 
feeding which must have an important place in the oyster investigations of the 
future. 

In order to remove the entire contents of the alimentary canal, I am now 
using the apparatus illustrated in figure 6, which is essentially a combination of 
stomach pump and enema, effectually irrigating the entire digestive tube. It 
consists of a reservoir (A), connected by a flexible siphon tube with a glass 
canula (B) ligated in the rectum, and of an aspirator (C) connected through the 
medium of a vial or test tube (D) with another canula (E) inserted in the mouth. 



FOOD AND FEEDING OF OYSTERS. 



1305 



The canulas are made of glass tubing, and their tips are held for a moment in a 

Bunsen flame to produce a burr, which prevents their slipping from the ligature. 

The operation of the apparatus is as follows: The reservoir (A) is lowered 

until the water surface is about level with the stage F. The oyster is carefully 




removed from its shell and placed on the stage, its rectum is slit for a distance of 
about one-eighth inch from the anus to facilitate the insertion of the canula, 
which is ligated in position by means of a needle and thread. The oral canula, 
which has a wider opening, is inserted in the mouth and ligated by means of a 



I3o6 BULLETIN OF THE BUREAU OF FISHERIES. 

needle and thread carried through the tissues. The pinch cock (G) is then 
released on the siphon of the aspirator, which exhausts the air from the vial or 
tube (D), draws out some of the stomach contents, and causes a slight collapse 
of the walls of the alimentary canal. The reservoir (A) is then raised until a 
flow of water is established through the rectum with a resultant slight turgescence 
of the intestine. There is thus established a current of water running into the 
rectum, through the intestine, and out of the mouth, carrying with it eventually 
the entire alimentary contents, which collect in the tube (D). To facilitate the 
dislodgment of the more or less impacted faeces, the intestine is occasionally 
gently tapped with the handle of a scalpel or dissecting needle. With one appa- 
ratus about six oysters per hour can be opened and operated on, and dissection 
shows the entire alimentary canal to be freed of contents. The contents of the 
tube are treated with a few drops of preservative and are concentrated, by pre- 
cipitation and the removal of the supernatent water, to a standard volume of 
5 or ID cubic centimeters, after which the organisms are counted by the Rafter 
method and the volume calculated as previously described. It is usual to take 
the average of five specimens as the measure of the food content of a given lot of 
oysters. 

For studying the rates of feeding of oysters under different environmental 
conditions, I have recently used the following experimental methods, which have 
been found effective : 

Pieces of sheet rubber (dentists' " rubber dam ") about 8 inches square, called 
" aprons, " are prepared by cutting out of the middle semicircular " windows " of 
about 2 inches radius, over which pieces of no. 25 bolting cloth are cemented 
with a thick ethereal solution of rubber. A slit about 5 inches long is cut in the 
rubber parallel to and about J^ inch below the long diameter of the window. 

A number of oysters, about 5 inches long, are then thoroughly scrubbed with 
a brush, washed in fresh water, the shells covered with a thin layer of Portland 
cement so as to fill all cavities and smooth irregularities in their surfaces, and 
thoroughly dried in the air. 

Each is then inserted in the slit in the middle of an " apron " in such position 
that the edges of the slit approximate the line running from the dorsal side of 
the hinge to the point of insertion of the gill at the edge of the mantle. The 
edges of the slit are then pasted to the shell with rubber solution, care being taken 
to provide a small fold in the apron at the lip of the shell, to carry it around the 
dorsal side of the hinge so as not to interfere with the opening of the valves, and 
to see that there are no gaps between the shell and the rubber at any point. 

Security of adhesion can be promoted by first giving the proper parts of the 
shell several coats of thin rubber solution, the final cementing being performed 
with a thick paste made by squeezing the ether-softened crude rubber through 
cheese cloth and reducing it to the desired consistency by shaking it in ether. 



FOOD AND FEEDING OF OYSTERS. 1307 

The oysters prepared in accordance with the foregoing description are then 
placed for about three days in filtered sea water, renewed morning and night, 
at the end of which time they are practically purged of food and usually gaping 
with hunger. The intestinal contents of five are then determined by means of 
the apparatus and methods already described. 

The remaining oysters are now placed each in a 6-inch Petri dish, the shells 
resting on a wire support to raise them above the bottom and lying so that the 
deep valve is downward and in such position that the cloacal or excurrent cham- 
ber of the oyster lies below the apron and the oral or incurrent chamber above 
it. The " apron " is then confined to the sides of the dish by means of a rubber 
band or cord, and a layer of sand is placed over the window and the surround- 
ing rubber to serve as a filter, as shown in figure 4. A piece of cheese cloth tied 
over the sand will prevent its being washed away by currents or disturbed by 
inquisitive fishes and crabs. 

When the oysters thus prepared are transferred to their natural environment 
they are as free to open their valves and feed as if they had never been removed 
from their beds; the oral chamber is in unobstructed communication with out- 
side waters while the excurrent chamber discharges into the Petri dish, where the 
faeces are retained while the expelled water passes through the filter. Oysters 
prepared as described have been kept under close observation under otherwise 
natural conditions and appeared to feed as freely and normally as neighboring 
specimens that had never been disturbed. The fseces drop into the dish in a 
little heap of demicylinders, while extraneous matter was excluded by the apron 
and filter. 

At the end of three and six days, respectively, lots of five of these oysters are 
taken up, their intestinal contents removed by the method already described and 
added to the faeces collected from the dishes. As about 95 per cent of the food 
consists of diatoms whose tests pass unchanged through the alimentary canal, 
it is evident that by calculating the volume of the combined food organisms of the 
faeces and alimentary canals by the methods described and deducting the 
volume of the residual intestinal contents, as determined from the lot of five 
starved check oysters, we can arrive at a volumetric expression of the average 
rate of feeding. Determinations of the diatomaceous content of the surrounding 
water made at intervals during the experiment supply the data for the necessary 
correction to be applied for dead diatom frustules ingested by the oysters under 
experiment. 

It is perhaps not necessary to use starved oysters for these experiments, but 
they have been used in order to insure the prompt commencement of feeding as 
soon as returned to the water, unstarved specimens sometimes "sulking" 
after repeated handling. A check upon possible error due to any abnormal 



I308 BULLETIN OF THE BUREAU OF FISHERIES. 

appetite at the beginning of the experiment is provided by comparison of the 
results obtained in the two lots fed for different periods. 

My first experiments were with bolting cloth aprons, but it was found diffi- 
cult to keep them covered with sand, especially close to the edges of the dish, 
and also to secure good adhesion between the shell and the apron. These 
defects in some cases permitted the infiltration of fine mud and other extraneous 
matter. Such difficulties have been obviated by the use of sheet-rubber 
" aprons " as described. The latter have been in use for four or five months and 
have proved satisfactory, but there has not been time for the tabulation of the 
quantitative results. 

It is believed that the apparatus and methods of research above described 
furnish for the first time efficient instruments for strictly qtiantitative studies 
of the food and feeding of oysters and similar mollusca, and they also furnish 
data for determining the amount of water filtered through the gills. In addition 
to the scientific interest attaching to the studies it is believed that they will lay 
the foundation for valuable economic data. As is well known to those who have 
made a study of the oyster fisheries, much time and money is lost in futile 
attempts to grow oysters in localities which eventually prove unsuitable. In 
many cases these failures are due to a paucity of food, the oysters failing to 
fatten. If there could be determined the minimum food unit requisite under 
varying conditions of bottom, currents, and density of oyster population, the 
waste of time, money, and effort in useless planting could be largely prevented. 

As a preliminary to the determination of such unit, it is necessary to deter- 
mine with accuracy the relations existing between the oysters and the plants 
which constitute their diet. We must know the exact relation existing between 
the food consumed by oysters which are rapidly growing and fattening and by 
those which are not. We must determine how much more food an oyster will 
consume in strong currents than when living in sluggish waters equally rich per 
unit of volume, and it will be necessary to learn also the water food content 
required to supply the minimum requisite under varying conditions of current. 

The experiments already conducted have shown that all of these data can 
be obtained with considerable accuracy by the means above described, and by 
conducting further research in regions such as Lynnhaven Bay, where the 
quantity of oysters on the bottom over considerable areas can be approximately 
arrived at, they can be given concrete application. The fornmlation of the 
desired unit will require much patient research and observation, the study of 
currents, of the behavior of oysters under various natural conditions, and pos- 
sibly of the reproductive activity of diatoms and other food organisms, but it is 
believed that we are now in possession of instruments which warrant an attempt 
at the solution of the problem. 



BuL. U. vS. B. F., 1908. 



Plate CXXV 




mSsm, 




